I've been asked about it a few times. So I decided to write a short snippet and example.

How do we define what "fixed" is?

The solution I found was to have the maximum zoom level constraint linked to the marker symbol's pixels. So if the maximum zoom level is constrained to "23", then define the height and width for your marker symbol at that level.

For my sample code above, I exaggerated it quite a bit and went for max zoom level of 24 and image height/width 40,000 pixels.